Do produce thumbnails of thumbnails, but in memory

fiv-browser.c

@@ -729,17 +729,6 @@ thumbnailers_start(FivBrowser *self)
 	if (!self->model)
 		return;
 
-	// TODO(p): Leave out all paths containing .cache/thumbnails altogether.
-	gchar *thumbnails_dir = fiv_thumbnail_get_root();
-	GFile *thumbnails = g_file_new_for_path(thumbnails_dir);
-	g_free(thumbnails_dir);
-
-	GFile *current = fiv_io_model_get_location(self->model);
-	gboolean is_a_thumbnail = current && g_file_has_prefix(current, thumbnails);
-	g_object_unref(thumbnails);
-	if (is_a_thumbnail)
-		return;
-
 	GList *missing = NULL, *lq = NULL;
 	for (guint i = self->entries->len; i--; ) {
 		Entry *entry = &g_array_index(self->entries, Entry, i);
@@ -988,7 +977,6 @@ fiv_browser_realize(GtkWidget *widget)
 		attributes.event_mask |= GDK_SMOOTH_SCROLL_MASK;
 
 	// We need this window to receive input events at all.
-	// TODO(p): See if input events bubble up to parents.
 	GdkWindow *window = gdk_window_new(gtk_widget_get_parent_window(widget),
 		&attributes, GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL);
 	gtk_widget_register_window(widget, window);

fiv-thumbnail.c

@@ -25,6 +25,7 @@
 #include <errno.h>
 #include <math.h>
 #include <stdbool.h>
+#include <string.h>
 
 #include "fiv-io.h"
 #include "fiv-thumbnail.h"
@@ -93,7 +94,7 @@ mark_thumbnail_lq(cairo_surface_t *surface)
 		surface, &fiv_thumbnail_key_lq, (void *) (intptr_t) 1, NULL);
 }
 
-gchar *
+static gchar *
 fiv_thumbnail_get_root(void)
 {
 	gchar *cache_dir = get_xdg_home_dir("XDG_CACHE_HOME", ".cache");
@@ -102,6 +103,23 @@ fiv_thumbnail_get_root(void)
 	return thumbnails_dir;
 }
 
+static gboolean
+might_be_a_thumbnail(const char *path_or_uri)
+{
+	// It is generally difficult to discern case in/sensitivity of subpaths,
+	// so err on the side of false positives.
+	gchar *normalized = g_ascii_strdown(path_or_uri, -1);
+
+	// The Windows path separator must be percent-encoded in URIs,
+	// and the file scheme always uses forward slashes.
+	if (G_DIR_SEPARATOR != '/')
+		g_strdelimit(normalized, G_DIR_SEPARATOR_S, '/');
+
+	gboolean matches = strstr(normalized, "/.cache/thumbnails/") != NULL;
+	g_free(normalized);
+	return matches;
+}
+
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
 static cairo_surface_t *
@@ -440,8 +458,10 @@ fiv_thumbnail_produce(GFile *target, FivThumbnailSize max_size, GError **error)
 	g_return_val_if_fail(max_size >= FIV_THUMBNAIL_SIZE_MIN &&
 		max_size <= FIV_THUMBNAIL_SIZE_MAX, FALSE);
 
+	// Don't save thumbnails for FUSE mounts, such as sftp://.
+	// Moreover, it doesn't make sense to save thumbnails of thumbnails.
 	const gchar *path = g_file_peek_path(target);
-	if (!path || !g_file_is_native(target) /* Don't save sftp://. */)
+	if (!path || !g_file_is_native(target) || might_be_a_thumbnail(path))
 		return produce_fallback(target, max_size, error);
 
 	// Make the TOCTTOU issue favour unnecessary reloading.
@@ -620,6 +640,11 @@ fiv_thumbnail_lookup(const char *uri, gint64 mtime_msec, FivThumbnailSize size)
 	g_return_val_if_fail(size >= FIV_THUMBNAIL_SIZE_MIN &&
 		size <= FIV_THUMBNAIL_SIZE_MAX, NULL);
 
+	// Don't waste time looking up something that shouldn't exist--
+	// thumbnail directories tend to get huge, and syscalls are expensive.
+	if (might_be_a_thumbnail(uri))
+		return NULL;
+
 	gchar *sum = g_compute_checksum_for_string(G_CHECKSUM_MD5, uri, -1);
 	gchar *thumbnails_dir = fiv_thumbnail_get_root();
 

fiv-thumbnail.h

@@ -52,9 +52,6 @@ extern FivThumbnailSizeInfo fiv_thumbnail_sizes[FIV_THUMBNAIL_SIZE_COUNT];
 /// If non-NULL, indicates a thumbnail of insufficient quality.
 extern cairo_user_data_key_t fiv_thumbnail_key_lq;
 
-/// Returns this user's root thumbnail directory.
-gchar *fiv_thumbnail_get_root(void);
-
 /// Attempts to extract any low-quality thumbnail from fast targets.
 /// If `max_size` is a valid value, the image will be downscaled as appropriate.
 cairo_surface_t *fiv_thumbnail_extract(